Centrifugal separation method for separating fluid components

ABSTRACT

An apparatus and method are provided for separating components of a fluid or particles. A separation vessel having a barrier dam is provided to initially separate an intermediate density components of a fluid, and a fluid chamber is provided to further separate these intermediate density components by forming an elutriative field or saturated fluidized particle bed. The separation vessel includes a shield for limiting flow into the fluid chamber of relatively high density substances, such as red blood cells. The separation vessel also includes a trap dam with a smooth, gradually sloped downstream section for reducing mixing of substances. Structure is also provided for adding additional plasma to platelets and plasma flowing from the fluid chamber. The system reduces clumping of platelets by limiting contact between the platelets and walls of the separation vessel.

This is a divisional of application Ser. No. 09/270,105, filed Mar. 16,1999 now U.S. Pat. No. 6,334,842, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for separatingcomponents of a fluid. The invention has particular advantages inconnection with separating blood components.

This application is related to U.S. Pat. No. 5,674,173, issued on Oct.7, 1997, U.S. patent application Ser. No. 08/676,039, filed on Jul. 5,1996 (pending), and U.S. patent application Ser. No. 08/853,374, filedon May 8,1997 (pending). The entire disclosures of U.S. Pat. No.5,674,173 and U.S. patent applications Ser. Nos. 08/676,039 and08/853,374 are incorporated herein by reference.

2. Description of the Related Art

In many different fields, liquids carrying particle substances must befiltered or processed to obtain either a purified liquid or purifiedparticle end product. In its broadest sense, a filter is any devicecapable of removing or separating particles from a substance. Thus, theterm “filter” as used herein is not limited to a porous media materialbut includes many different types of processes where particles areeither separated from one another or from liquid.

In the medical field, it is often necessary to filter blood. Whole bloodconsists of various liquid components and particle components.Sometimes, the particle components are referred to as “formed elements”.The liquid portion of blood is largely made up of plasma, and theparticle components include red blood cells (erythrocytes), white bloodcells (including leukocytes), and platelets (thrombocytes). While theseconstituents have similar densities, their average density relationship,in order of decreasing density, is as follows: red blood cells, whiteblood cells, platelets, and plasma. In addition, the particleconstituents are related according to size, in order of decreasing size,as follows: white blood cells, red blood cells, and platelets. Mostcurrent purification devices rely on density and size differences orsurface chemistry characteristics to separate and/or filter the bloodcomponents.

Numerous therapeutic treatments require groups of particles to beremoved from whole blood before either liquid or particle components canbe infused into a patient. For example, cancer patients often requireplatelet transfusions after undergoing ablative, chemical, or radiationtherapy. In this procedure, donated whole blood is processed to removeplatelets and these platelets are then infused into the patient.However, if a patient receives an excessive number of foreign whiteblood cells as contamination in a platelet transfusion, the patient'sbody may reject the platelet transfusion, leading to a host of serioushealth risks.

Typically, donated platelets are separated or harvested from other bloodcomponents using a centrifuge. The centrifuge rotates a blood reservoirto separate components within the reservoir using centrifugal force. Inuse, blood enters the reservoir while it is rotating at a very rapidspeed and centrifugal force stratifies the blood components, so thatparticular components may be separately removed. Centrifuges areeffective at separating platelets from whole blood, however theytypically are unable to separate all of the white blood cells from theplatelets. Historically, blood separation and centrifugation devices aretypically unable to consistently (99% of the time) produce plateletproduct that meets the “leukopoor” standard of less than 5×10⁶ whiteblood cells for at least 3×10¹¹ platelets collected.

Because typical centrifuge platelet collection processes are unable toconsistently and satisfactorily separate white blood cells fromplatelets, other processes have been added to improve results. In oneprocedure, after centrifuging, platelets are passed through a porouswoven or non-woven media filter, which may have a modified surface, toremove white blood cells. However, use of the porous filter introducesits own set of problems. Conventional porous filters may be inefficientbecause they may permanently remove or trap approximately 5-20% of theplatelets. These conventional filters may also reduce“plateletviability,” meaning that once passed through a filter a percentage ofthe platelets cease to function properly and may be partially or fullyactivated. In addition, porous filters may cause the release ofbrandykinin, which may lead to hypotensive episodes in a patient. Porousfilters are also expensive and often require additional time consumingmanual labor to perform a filtration process.

Although porous filters are effective in removing a substantial numberof white blood cells, they have drawbacks. For example, aftercentrifuging and before porous filtering, a period of time must pass togive activated platelets time to transform to a deactivated state.Otherwise, the activated platelets are likely to clog the filter.Therefore, the use of at least some porous filters is not feasible inon-line processes.

Another separation process is one known as centrifugal elutriation. Thisprocess separates cells suspended in a liquid medium without the use ofa membrane filter. In one common form of elutriation, a cell batch isintroduced into a flow of liquid elutriation buffer. This liquid whichcarries the cell batch in suspension, is then introduced into afunnel-shaped chamber located in a spinning centrifuge. As additionalliquid buffer the chamber, the liquid sweeps smaller sized,slower-sedimenting cells toward an elutriation boundary within thechamber, while larger, faster-sedimenting cells migrate to an area ofthe chamber having the greatest centrifugal force.

When the centrifugal force and force generated by the fluid flow arebalanced, the fluid flow is increased to force slower-sedimenting cellsfrom an exit port in the chamber, while faster-sedimenting cells areretained in the chamber. If fluid flow through the camber is increased,progressively larger, faster-sedimenting cells may be removed from thechamber.

Thus, centrifugal elutriation separates particles having differentsedimentation velocities. Stoke's law describes sedimentation velocity(SV) of a spherical particle as follows:${SV} = {\frac{2}{9}\frac{r^{2}\left( {\rho_{p} - \rho_{m}} \right)g}{\eta}}$

where, r is the radius of the particle, ρ_(p) is the density of theparticle, ρ_(m) is the density of the liquid medium, η is the viscosityof the medium, and g is the gravitational or centrifugal acceleration.Because the radius of a particle is raised to the second power in theStoke's equation and the density of the particle is not, the size of acell, rather than its density, greatly influences its sedimentationrate. This explains why larger particles generally remain in a chamberduring centrifugal elutriation, while smaller particles are released, ifthe particles have similar densities.

As described in U.S. Pat. No. 3,825,175 to Sartory, centrifugalelutriation has a number of limitations. In most of these processes,particles must be introduced within a flow of fluid medium in separatediscontinuous batches to allow for sufficient particle separation. Thus,some elutriation processes only permit separation in particle batchesand require an additional fluid medium to transport particles. Inaddition, flow forces must be precisely balanced against centrifugalforce to allow for proper particle segregation.

Further, a Coriolis jetting effect takes place when particles flow intoan elutriation chamber from a high centrifugal field toward a lowercentrifugal field. The fluid and particles turbulently collide with aninner wall of the chamber facing the rotational direction of thecentrifuge. This phenomenon mixes particles within the chamber andreduces the effectiveness of the separation process. Further, Coriolisjetting shunts flow along the inner wall from the inlet directly to theoutlet. Thus, particles pass around the elutriative field to contaminatethe end product.

Particle mixing by particle density inversion is an additional problemencountered in some prior elutriation processes. Fluid flowing withinthe elutriation chamber has a decreasing velocity as it flows in thecentripetal direction from an entrance port toward an increased crosssectional portion of the chamber. Because particles tend to concentratewithin a flowing liquid in areas of lower flow velocity, rather than inareas of high flow velocity, the particles concentrate near theincreased cross-sectional area of the chamber. Correspondingly, sinceflow velocity is greatest adjacent the entrance port, the particleconcentration is reduced in this area. Density inversion of particlestakes place when the centrifugal force urges the particles from the highparticle concentration at the portion of increased cross-section towardthe entrance port. This particle turnover reduces the effectiveness ofparticle separation by elutriation.

For these and other reasons, there is a need to improve particleseparation.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus and method thatsubstantially obviate one or more of the limitations and disadvantagesof the related art. To achieve these and other advantages and inaccordance with the purpose of the invention, as embodied and broadlydescribed herein, the invention includes an apparatus for use with acentrifuge having a rotatable rotor including a retainer. The apparatuscomprises a separation vessel for placement in the retainer. Theseparation vessel has an inlet portion, an outlet portion, and a flowpath extending between the inlet portion and the outlet portion. Theinlet portion has an inlet port for supplying to the separation vessel afluid to be separated into components. The outlet portion includes afirst wall, a second wall spaced from the first wall, at least threeoutlet ports for removing separated components of the fluid from theseparation vessel, and a shield between one of the outlet ports and thesecond wall for limiting entry into said one outlet port of at least onerelatively high density component of the fluid. The shield has a surfacefacing said one outlet port. When the separation vessel is placed in theretainer, the surface of the shield is located closer than two of theother outlet ports to the axis of rotation to maintain the surface ofthe shield out of a layer of the relatively high density fluid componentformed in the outlet portion.

In one other aspect, the invention includes a centrifugal separationapparatus having a centrifuge rotor, a retainer on the centrifuge rotor,and a separation vessel in the retainer. The separation vessel includesan inlet portion, an outlet portion, and a trap dam. The outlet portionhas a barrier for substantially blocking passage of at least one of theseparated components of the fluid, and at least one outlet port forremoving at least the blocked component of the fluid from the vessel.The trap dam is located between the outlet port and the inlet portion.The trap dam extends away from the axis of rotation of the rotor to traprelatively low density substances and includes a downstream portionhaving a relatively gradual slope.

In an additional aspect, the separation vessel further includes agradual sloped segment across from the trap dam. The gradual slopedsegment increases thickness of a layer of the relatively high densityfluid component formed across from the trap dam.

In another aspect, the invention includes an apparatus having aseparation vessel and a fluid chamber. The separation vessel includes aninlet port, a first outlet port for removing at least relativelyintermediate density components of fluid, and a second outlet port forremoving at least one relatively low density component of the fluid. Afirst line is coupled to the first outlet port and also is coupled to aninlet of a fluid chamber for separating the components of the fluidflowing through the first line. A second line is coupled to the secondoutlet port and is also in flow communication with an outlet of thefluid chamber to mix the relatively low density component of the fluidwith substances flowing from the outlet of the fluid chamber.

In yet another aspect, the invention includes a method of separatingcomponents of a fluid. In the method, a separation vessel rotates aboutan axis of rotation and fluid to be separated passes into the vessel.The fluid separates into at least a relatively high density component, arelatively intermediate density component, and a relatively low densitycomponent. At least the relatively intermediate density component isremoved from the separation vessel via an outlet port. Passage of therelatively high density component into the outlet port is limited with ashield having a surface facing the outlet port. The position of aninterface between the high density component and the intermediatedensity component is controlled so that the surface of the shield isbetween the interface and the outlet port.

In still another aspect, the high density component includes red bloodcells, the intermediate density component includes platelets, and thelow density component includes plasma.

In an additional aspect, the invention includes a method wherein atleast relatively intermediate density components are removed from theseparation vessel via a first outlet port; and at least some of a lowdensity component is removed from the separation vessel via a secondoutlet port. The removed intermediate density components are flowed intoa fluid chamber. At least some of a first subcomponent of theintermediate density components is retained in the fluid chamber, and atleast some of a second subcomponent of the intermediate densitycomponents is permitted to flow from an outlet of the fluid chamber. Thelow density component removed from the separation vessel is combinedwith the second subcomponent flowing from the outlet of the fluidchamber.

In a further aspect of the invention, the first subcomponent includeswhite blood cells, the second subcomponent includes platelets, and thelow density component includes plasma.

In an even further aspect of the invention, an apparatus for use with acentrifuge includes a separation vessel having an outlet portionincluding at least one outlet port and a shield having a surface facingthe outlet port. Structure is provided for controlling the position ofan interface between at least one relatively high density component of afluid and at least one other separated component of the fluid so thatthe surface of the shield is between the interface and the outlet port.

In another aspect, the invention includes a method of reducing clumpingof platelets during separation of blood components. The method includesintroducing blood components into a rotating separation vessel such thatthe blood components stratify in the separation vessel to form at leasta radial outer layer including red blood cells, an intermediate layerincluding at least platelets, and a radial inner layer including lowdensity substances. To substantially limit contact between the plateletsand at least one of the radial inner and outer walls of the separationvessel, the radial outer layer of red blood cells is maintained betweenthe intermediate layer and the radial outer wall of the separationvessel and/or the radial inner layer of low density substances ismaintained between the intermediate layer and the radial inner wall ofthe separation vessel. This reduces platelet clumping.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 is a partial perspective view of a centrifuge apparatus includinga fluid chamber in accordance with an embodiment of the invention;

FIG. 2 is a partial cross-sectional, schematic view of a portion of aseparation vessel and the fluid chamber mounted on the rotor of FIG. 1during a separation procedure;

FIG. 3 is a cross-sectional view of inlet and outlet portions of aconventional separation vessel;

FIG. 4. is a perspective view of a tubing set including the fluidchamber and an alternative embodiment of the separation vessel;

FIG. 5 is a partial cross sectional view of inlet and outlet portions ofthe separation vessel and fluid chamber of FIG. 4 on a rotor;

FIG. 6 is a view like that of FIG. 5 showing radial spacing ofstructural features; and

FIG. 7 is a view similar to FIG. 5 of another alternative embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention illustrated in the accompanying drawings.Wherever possible, the same reference numbers are used in the drawingsand the description to refer to the same or like parts, and the samereference numerals with alphabetical suffixes are used to refer tosimilar parts.

The embodiments of the present invention preferably include a COBE®SPECTRA™ single stage blood component centrifuge manufactured by CobeLaboratories of Colorado. The COBE® SPECTRA™ centrifuge incorporates aone-omega/two-omega sealless tubing connection as disclosed in U.S. Pat.No. 4,425,112 to Ito, the entire disclosure of which is incorporatedherein by reference. The COBE® SPECTRA™ centrifuge also uses asingle-stage blood component separation channel substantially asdisclosed in U.S. Pat. No. 4,094,461 to Kellogg et al. and U.S. Pat. No.4,647,279 to Mulzet et al., the entire disclosures of which are alsoincorporated herein by reference. The embodiments of the invention aredescribed in combination with the COBE® SPECTRA™ centrifuge for purposesof discussion only, and this is not intended to limit the invention inany sense.

As will be apparent to one having skill in the art, the presentinvention may be advantageously used in a variety of centrifuge devicescommonly used to separate blood into its components. In particular, thepresent invention may be used with any centrifugal apparatus thatemploys a component collect line such as a platelet collect line or aplatelet rich plasma line, whether or not the apparatus employs a singlestage channel or a one-omega/two-omega sealless tubing connection.

As embodied herein and illustrated in FIG. 1, the present inventionincludes a centrifuge apparatus 10 having a centrifuge rotor 12 coupledto a motor 14 so that the centrifuge rotor 12 rotates about its axis ofrotation A—A. The rotor 12 has a retainer 16 including a passageway orannular groove 18 having an open upper surface adapted to receive aseparation vessel 28, 28 a, or 28 b shown respectively in FIGS. 2, 4-6,and 7. The groove 18 completely surrounds the rotor's axis of rotationA—A and is bounded by an inner wall 20 and an outer wall 22 spaced apartfrom one another to define the groove 18 therebetween. Although thegroove 18 shown in FIG. 1 completely surrounds the axis of rotation A—A,the groove could be partially around the axis A—A when the separationvessel is not generally annular. As compared to previous designs of theCOBE® SPECTRA™ blood component centrifuge, the outer wall 22 ispreferably spaced closer to the axis of rotation A—A to reduce thevolume of the separation vessel 28, 28 a, 28 b and to increase flowvelocity in the vessel 28, 28 a, 28 b.

Preferably, a substantial portion of the groove 18 has a constant radiusof curvature about the axis of rotation A—A and is positioned at amaximum possible radial distance on the rotor 12. As described below,this shape ensures that substances separated in the separation vessel28, 28 a, 28 b undergo relatively constant centrifugal forces as theypass from an inlet portion to an outlet portion of the separation vessel28, 28 a, 28 b.

The motor 14 is coupled to the rotor 12 directly or indirectly through ashaft 24 connected to the rotor 12. Alternately, the shaft 24 may becoupled to the motor 14 through a gearing transmission (not shown).

As shown in FIG. 1, a holder 26 is provided on a top surface of therotor 12. The holder 26 releasably holds a fluid chamber 30 on the rotor12 so that an outlet 32 of the fluid chamber 30 is positioned closer tothe axis of rotation A—A than an inlet 34 of the fluid chamber 30. Theholder 26 preferably orients the fluid chamber 30 on the rotor 12 with alongitudinal axis of the fluid chamber 30 in a plane transverse to therotor's axis of rotation A—A. In addition, the holder 26 is preferablyarranged to hold the fluid chamber 30 on the rotor 12 with the fluidchamber outlet 32 facing the axis of rotation A—A. Although the holder26 retains the fluid chamber 30 on a top surface of the rotor 12, thefluid chamber 30 may also be secured to the rotor 12 at alternatelocations, such as beneath the top surface of the rotor 12.

FIG. 2 schematically illustrates a portion of the separation vessel 28and fluid chamber 30 mounted on the rotor 12., The separation vessel 28has a generally annular flow path 46 and includes an inlet portion 48and outlet portion 50. A wall 52 prevents substances from passingdirectly between the inlet and outlet portions 48 and 50 without firstflowing around the generally annular flow path 46 (e.g.,counterclock-wise as illustrated by arrows in FIG. 2).

In the portion of the separation vessel 28 between the inlet and outletportions 48 and 50, a radial outer wall 65 of the separation vessel 28is preferably positioned closer to the axis of rotation A—A than theradial outer wall 65 in the outlet portion 50. During separation ofblood components in the separation vessel 28, this arrangement causesformation of a very thin and rapidly advancing red blood cell bed in theseparation vessel 28 between the inlet and outlet portions 48 and 50.The red blood cell bed reduces the amount of blood components requiredto initiate a separation procedure, and also decrease the number ofunnecessary red blood cells in the separation vessel 28. As explainedbelow, the radially outer red blood cell bed substantially limits, ormore preferably prevents, platelets from contacting the radial outerwall 65 of the separation vessel 28. This is believed to reduce clumpingof platelets caused when platelets contact structural components ofcentrifugal separation devices, which are normally formed of polymermaterials.

As shown in FIG. 2, the inlet portion 48 includes an inflow tube 36 forconveying a fluid to be separated, such as whole blood, into theseparation vessel 28. The outlet portion 50, on the other hand, includesfirst, second, and third outlet lines 38, 40, 42 for removing separatedsubstances from the separation vessel 28 and an interface control line44 for adjusting the level of an interface F between separatedsubstances in the vessel 28. Preferably, the separation vessel 28 formswhat is known as a single stage component separation area rather thanforming a plurality of such stages. In other words, each of thecomponents separated in the vessel 28 preferably are collected andremoved in only one area of the vessel 28, namely the outlet portion 50.In addition, the separation vessel 28 preferably includes asubstantially constant radius except in the region of the outlet portion50 where the outer wall of the outlet portion 50 is preferablypositioned farther away from the axis of rotation A—A to allow foroutlet ports 56, 58, 60, and 61 of the lines 38, 40, 42, and 44,respectively, to be positioned at different radial distances and tocreate a collection pool with greater depth for the high density redblood cells.

Although the lines 38, 40, and 42 are referred to as being“collection”lines, the substances removed through these lines can be eithercollected or reinfused back into a donor. In addition, the inventioncould be practiced without one or more of the lines 40, 42, and 44.

Although FIG. 2 shows the inlet portion 48 as having a wide radialcross-section, the outer wall of the inlet portion 48 can be spacedcloser to the inner wall of the inlet portion 48 and/or be tapered. Aninlet port 54 of inflow tube 36 allows for flow of a substance to beseparated, such as whole blood, into the inlet portion 48 of separationvessel 28. During a separation procedure, substances entering the inletportion 48 follow the flow path 46 and stratify according to differencesin density in response to rotation of the rotor 12. Preferably, the flowpath 46 between the inlet and outlet portions 48 and 50 is curved andhas a substantially constant radius. In addition, the flow path 46 isplaced at the maximum distance from the axis A—A. This shape ensuresthat components passing through the flow path 46 encounter a relativelyconstant gravitational field and a maximum possible gravitational fieldfor the rotor 12.

The separated substances flow into the outlet portion 50 where they areremoved via first, second, and third outlet ports 56, 58, and 60respectively, of first, second, and third collection lines 38, 40, and42. Separated substances are also removed by an interface controllingoutlet port 61 of the interface control line 44.

As shown in FIG. 2, the first, second, and third ports 56, 58, and 60and interface port 61 are positioned at varying radial locations on therotor 12 to remove substances having varying densities. The secondoutlet port 58 is farther from the axis of rotation A—A than the first,third, and interface ports 56, 60 and 61 to remove higher densitycomponents H separated in the separation vessel 28, such as red bloodcells. The third port 60 is located closer to the axis of rotation A—Athan the first, second, and interface ports 56, 58, and 61 to remove theleast dense components L separated in the separation vessel 28, such asplasma. Preferably, the first port 56 is about .035 inch to about 0.115inch closer than the interface port 61 to the axis of rotation A—A.

As shown in FIG. 2, the outlet portion 50 includes a barrier 62 forsubstantially blocking flow of intermediate density components 1, suchas platelets and some mononuclear cells (white blood cells). Preferably,the barrier 62 is a skimmer dam extending completely across the outletportion 50 in a direction generally parallel to the axis of rotationA—A. The first outlet port 56 is positioned immediately upstream frombarrier 62, downstream from the inlet portion 48, to collect at leastthe intermediate density components I blocked by the barrier 62 and,optionally, some of the lower density components L.

Radially inner and outer edges of the barrier 62 are spaced fromradially inner and outer walls 63, 65 of the separation vessel 28 toform a first passage 64 for lower density components L, such as plasma,at a radially inner position in the outlet portion 50 and a secondpassage 66 for higher density components H, such as red blood cells, ata radially outer position in the outlet portion 50. The second and thirdcollection ports 58 and 60 are preferably positioned downstream from thebarrier 62 to collect the respective high and low density components Hand L passing through the second and first passages 66 and 64.

The interface control outlet port 61 is also preferably positioneddownstream from the barrier 62. During a separation procedure, theinterface port 61 removes the higher density components H and/or thelower density components L in the outlet portion 50 to thereby controlthe radial position of the interface F between the intermediate densitycomponents I and higher density components H in the outlet portion 50 sothat the interface F and the interface port 61 are at about the sameradial distance from the rotational axis A—A. Although the interfaceport 61 is the preferred structure for controlling the radial positionof the interface F, alternative structure could be provided forperforming this function. For example, the position of the interface Fcould be controlled without using an interface port by providing anoptical monitor (not shown) for monitoring the position of the interfaceand controlling flow of liquid and/or particles through one or more ofthe ports 54, 56, 58, and 60 in response to the monitored position.

Preferably, the second collection line 40 is flow connected to theinterface control line 44 so that substances removed via the secondcollection port 58 and the interface control port 61 are combined andremoved together through a common line. Although the second and thirdoutlet ports 58 and 60 and the interface outlet port 61 are showndownstream from the barrier 62, one or more of these ports may beupstream from the barrier 62. In addition, the order of the outlet ports56, 58, 60, and the control port 61 along the length of the outletportion 50 could be changed. Further details concerning the structureand operation of the separation vessel 28 are described in U.S. Pat. No.4,094,461 to Kellogg et al. and U.S. Pat. No. 4,647,279 to Mulzet etal., which have been incorporated herein by reference.

A shield 96 is positioned between the first outlet port 56 and the outerwall 65 to limit entry into the first outlet port 56 of the higherdensity components H. The shield 96 is preferably a shelf extending froman upstream side of the dam 62. In the preferred embodiment, the shield96 is at least as wide (in a direction parallel to the axis A—A) as thefirst outlet port 56 and extends upstream at least as far as theupstream end of first outlet port 56 so that the shield 96 limits directflow into the first outlet port 56 of components residing between theshield 96 and the outer wall 65, including the higher density componentsH. In other words, the shield 96 ensures that a substantial amount ofthe substances flowing into the first outlet port 56 originate fromradial locations which are not further than the shield 96 from the axisof rotation A—A.

Preferably, the shield 96 has a radially inner surface 98 facing thefirst outlet port 56. The inner surface 98 is spaced radially outwardfrom the first outlet port 56 by a distance of preferably from about0.005 inch to about 0.08 inch, and more preferably from about 0.02 inchto about 0.03 inch. The inner surface 98 is positioned farther than thefirst and third outlet ports 56 and 60 from the axis of rotation A—A.The inner surface 98 is also positioned closer than the second outletport 58 and the interface outlet port 61 to the axis of rotation A—A.The relative positioning of the inner surface 98 and interface outletport 61 maintains the inner surface 98 above the interface F, out of thelayer of the higher density components H formed in the outlet portion50, and in the layer of intermediate density components 1. Because thetop surface 98 is above the interface F, the shield 96 blocks flow ofhigher density substances H into the first outlet port 56. When theseparation vessel 28 is used in a blood component procedure where thelayer of higher density substances H primarily includes red blood cells,preferably the shield 96 significantly reduces the number of red bloodcells which flow into the first outlet port 56.

FIG. 3 shows a view of a portion of a conventional separation vessel 28′disclosed in above-mentioned U.S. Pat. No. 4,647,279 to Mulzet et al. Asshown in FIG. 3, this separation vessel 28′ includes a first outlet 56′for intermediate density substances, a second outlet 58′ for highdensity substances, a third outlet 60′ for low density substances, andan interface control outlet 61′. In addition, the separation vessel 28′includes a barrier 62′ having a flow directer 100 positioned radiallyoutward from the outlet 56′. However, the flow directer 100 does notsiginificantly reduce flow of high density substances, such as red bloodcells, into the outlet 56′ because the flow directer 100 has a radiallyinner surface 102 which is located radially outward from the interfacecontrol port 61′ to position the inner surface 102 in a layer of higherdensity substances. In other words, the radially inner surface 102 islocated radially outward from an interface between higher densitysubstances and intermediate density substances formed in the separationvessel 28′.

As shown in FIGS. 1 and 2, the preferred embodiment of the presentinvention preferably includes a ridge 68 extending from the inner wall20 of the groove 18 toward the outer wall 22 of the groove 18. When theseparation vessel 28 shown in FIG. 2 is loaded in the groove 18, theridge 68 deforms semi-rigid or flexible material in the outlet portion50 of the separation vessel 28 to form a trap dam 70 on the radiallyinner wall 63 of the separation vessel 28, upstream from the firstcollection port 56. The trap dam 70 extends away from the axis ofrotation A—A to trap a portion of lower density substances, such aspriming fluid and/or plasma, along a radially inner portion of theseparation vessel 28 located upstream the trap dam 70.

When the separation vessel 28 is used to separate whole blood into bloodcomponents, the trap dam 70 traps priming fluid (i.e. saline) and/orplasma along the inner wall 63 and these trapped substances help conveyplatelets to the outlet portion 50 and first collection port 56 byincreasing plasma flow velocities next to the layer of red blood cellsin the separation vessel 28 to scrub platelets toward the outlet portion50. As explained below, the trapped priming fluid and/or plasma alongthe inner wall 63 also substantially limits, or more preferablyprevents, platelets from contacting the radial inner wall 63. This isbelieved to reduce clumping of platelets caused when platelets contactstructural components of centrifugal separation devices, which arenormally formed of polymer materials.

Preferably, the trap dam 70 has a relatively smooth surface to limitdisruption of flow in the separation vessel 28, for example, by reducingCoriolis forces. In the preferred embodiment, a downstream portion 104of the trap dam 70 has a relatively gradual slope extending in thedownstream direction toward the axis of rotation A—A. During a bloodcomponent separation procedure, the relatively gradual slope of thedownstream portion 104 limits the number of platelets (intermediatedensity components) that become reentrained (mixed) with plasma (lowerdensity components) as plasma flows along the trap dam 70. In addition,the gradual sloped shape of the downstream portion 104 reduces thenumber of platelets that accumulate in the separation vessel 28 beforereaching the first collection port 56.

As shown in FIG. 2, the gradual slope of the downstream portion 104preferably extends to a downstream end 106 located closer than the firstoutlet port 56 to the axis of rotation A—A. When the separation vessel28 is used for blood component separation, the downstream end 106 ispreferably located radially inward from the layer of platelets formed inthe separation vessel 28. In contrast, when the downstream end 106 islocated radially outward from the radially innermost portion of theplatelet layer, plasma flowing along the surface of the dam 70 couldreentrain (mix) the platelets in plasma downstream from the dam,reducing the efficiency of blood component separation.

In the preferred embodiment shown in FIG. 2, the trap dam 70 and itsdownstream portion 104 preferably have a generally convex curvature.Preferably, the surface of the trap dam 70 is in the form of a constantradius arc having a center of curvature offset from the axis of rotationA—A. Although the trap dam 70 could have any radius of curvature, aradius of from about 0.25 inch to about 2 inches is preferred, and aradius of about 2 inches is most preferred.

Although the ridge 68 preferably deforms the separation vessel 28 toform the trap dam 70, the trap dam 70 could be formed in other ways. Forexample, the trap dam 70 could be a permanent structure extending from aradially inner wall of the separation vessel 28. In addition, the trapdam 70 could be positioned closer to the barrier 62 and have a smallhole passing therethrough to allow for passage of air in a radial innerarea of the outlet portion 50.

As shown in FIGS. 1 and 2, the outer wall 22 of the groove 18 preferablyincludes a gradual sloped portion 108 facing the ridge 68 in the innerwall 20. When the separation vessel 28 shown in FIG. 2 is loaded in thegroove 18, the gradual sloped portion 108 deforms semi-rigid or flexiblematerial in the outlet portion 50 of the separation vessel 28 to form arelatively smooth and gradual sloped segment 110 in a region of thevessel 28 across from the trap dam 70. In an alternative embodiment,this gradual sloped segment 110 is a permanent structure formed in theseparation vessel 28.

In the downstream direction, the segment 110 slopes gradually away fromthe axis of rotation A—A to increase the thickness of a layer of highdensity fluid components H, such as red blood cells, formed across fromthe trap dam 70. The gradual slope of the segment 110 maintainsrelatively smooth flow transitions in the separation vessel 28 andreduces the velocity of high density components H (red blood cells)formed radially outward from the intermediate density components I(platelets).

Preferably, an upstream end 112 of the gradual sloped segment 110 ispositioned upstream from the trap dam 70. This position of the upstreamend 112 reduces the velocity of high density components H, such as redblood cells, as these components flow past the trap dam 70 and formradially outward from the layer of intermediate density components Iblocked by the barrier 62.

As shown in FIG. 2, the first collection line 38 is connected betweenthe first outlet port 56 and the fluid chamber inlet 34 to pass theintermediate density components into the fluid chamber 30. Preferably,the fluid chamber 30 is positioned as close as possible to the firstoutlet port 56 so that any red blood cells entering the fluid chamber 30will be placed in a high gravitational field and compacted. As describedbelow, components initially separated in the separation vessel 28 arefurther separated in the fluid chamber 30. For example, white bloodcells could be separated from plasma and platelets in the fluid chamber30. This further separation preferably takes place by forming anelutriative field in the fluid chamber 30 or by forming a saturatedfluidized bed of particles, such as platelets, in the fluid chamber 30.

The fluid chamber 30 is preferably constructed similar or identical toone of the fluid chambers disclosed in above-mentioned U.S. patentapplication Ser. No. 08/676,039 and U.S. Pat. No. 5,674,173. As shown inFIG. 2, the inlet 34 and outlet 32 of the fluid chamber 30 are arrangedalong a longitudinal axis of the fluid chamber 30. A wall of the fluidchamber 30 extends between the inlet 34 and outlet 32 thereby definingthe inlet 34, the outlet 32, and an interior of the fluid chamber 30.

The fluid chamber 30 preferably includes two frustoconical shapedsections joined together at a maximum cross-sectional area of the fluidchamber 30. The interior of the fluid chamber 30 preferably tapers(decreases in cross-section) from the maximum cross-sectional area inopposite directions toward the inlet 34 and the outlet 32. Although thefluid chamber 30 is depicted with two sections having frustoconicalinterior shapes, the interior of each section may be paraboloidal, or ofany other shape having a major cross-sectional area greater than theinlet or outlet area.

The volume of the fluid chamber 30 should be at least large enough toaccommodate the formation of a saturated fluidized particle bed(described below) for a particular range of flow rates, particle sizes,and rotational speeds of the centrifuge rotor 12. The fluid chamber 30may be constructed from a unitary piece of plastic or from separatepieces joined together to form separate sections of the fluid chamber30. The fluid chamber 30 may be formed of a transparent or translucentcopolyester plastic, such as PETG, to allow viewing of the contentswithin the chamber interior with the aid of an optional strobe (notshown) during a separation procedure.

As shown in FIG. 2, a groove 72 is formed on an inner surface of thefluid chamber 30 at a position of the maximum cross-sectional area. Thegroove 72 is defined by top and bottom wall surfaces orientedsubstantially perpendicular to the longitudinal axis of the fluidchamber 30 and an inner surface of the fluid chamber 30 facing thelongitudinal axis. Preferably, the groove 72 is annular, however, thegroove 72 may also partially surround the longitudinal axis of the fluidchamber 30.

The groove 72 helps to disperse Coriolis jetting within the fluidchamber 30, as described below. Sudden increases in liquid flow rateduring a particle separation procedure may limit the effectiveness ofelutriative particle separation or may limit the ability of thesaturated fluidized particle bed to obstruct particle passage. Liquidflowing into the fluid chamber 30 undergoes a Coriolis jetting effect.This jetting flow reduces the filtration effectiveness of the saturatedfluidized particle bed because liquid and particles may pass between thesaturated fluidized particle bed and an interior wall surface of thefluid chamber 30 rather than into the bed itself. The fluid chamber 30including groove 72 counteracts these effects by channeling Coriolisjetting flow in a circumferential direction partially around the axis offluid chamber 30. Therefore, the groove 72 improves the particleobstruction capability of the saturated bed, especially when liquid flowrates increase.

As shown in FIG. 2, a circumferential lip 74 extends from a top portionof the groove 72 toward a bottom portion of the groove 72 to define anentrance into the groove 72. The lip 74 functions to guide fluid in thegroove 72.

A plurality of steps 76 are preferably formed on an inner surface of thefluid chamber 30 between the maximum cross-section of the chamber 30 andthe inlet 34. Although six steps 76 are illustrated, any number of stepsmay be provided in the fluid chamber 30.

Each step 76 has a base surface oriented substantially perpendicular tothe longitudinal axis of the fluid chamber 30, as well as a side surfacepositioned orthogonal to the base surface. Although FIG. 2 depicts acorner where the side surface and the base surface intersect, a concavegroove may replace this corner. In a preferred embodiment, each step 76is annular and surrounds the axis of the chamber 30 completely to bounda cylindrical shaped area. Alternative, the steps 76 may partiallysurround the axis of the chamber 30.

Adding steps 76 to the fluid chamber 30, also improves the particleobstruction characteristics of a saturated fluidized particle bed formedin the fluid chamber 30, in particular during increases in the rate offluid flow. The steps 76 provide this improvement by providing momentumdeflecting and redirecting surfaces to reduce Coriolis jetting in fluidchamber 30. When Coriolis jetting takes place, the liquid and particlesof the jet travel along an interior surface of the fluid chamber 30 thatfaces the direction of centrifuge rotation. Therefore, the jet maytransport particles between the fluid chamber interior surface andeither a saturated fluidized particle bed or an elutriation fieldpositioned in the fluid chamber 30. Thus, particles traveling in the jetmay exit the fluid chamber 30 without being separated.

Steps 76 direct or alter the momentum of the Coriolis jet flow of liquidand particles generally in a circumferential direction about the axis ofthe fluid chamber 30. Thus, a substantial number of particles originallyflowing in the jet must enter the saturated fluidized bed or elutriationfield to be separated.

The groove 72 and steps 76 are provided to facilitate fluid flow rateincreases, as well as to improve steady state performance of the fluidchamber 30. During blood component separation, the groove 72 and steps76 greatly reduce the number of white blood cells that would otherwisebypass a saturated fluidized platelet bed formed in the fluid chamber30.

As schematically shown in FIG. 2, a plurality of pumps 78, 80, 84 areprovided for adding and removing substances to and from the separationvessel 28 and fluid chamber 30. An inflow pump 78 is coupled to theinflow line 36 to supply a substance to be separated, such as wholeblood, to the inlet portion 48. A first collection pump 80 is coupled tooutflow tubing 88 connected to the fluid chamber outlet 32. The firstcollection pump 80 draws fluid and particles from the fluid chamberoutlet 32 and causes fluid and particles to enter the fluid chamber 30via the fluid chamber inlet 34.

A second collection pump 84 is flow coupled to the second collectionline 42 for removing substances through the third outlet port 60.Preferably, the second collection line 40 and interface control line 44are flow connected together, and substances flow through these lines 40and 44 as a result of positive fluid pressure in the vessel outletportion 50.

The pumps 78, 80, 84 are preferably peristaltic pumps or impeller pumpsconfigured to prevent significant damage to blood components. However,any fluid pumping or drawing device may be provided. In an alternativeembodiment (not shown), the first collection pump 80 may be fluidlyconnected to the fluid chamber inlet 34 to directly move substances intoand through the fluid chamber 30. The pumps 78, 80, 84 may be mounted atany convenient location.

As shown in FIG. 1, the apparatus 10 further includes a controller 89connected to the motor 14 to control rotational speed of the rotor 12.In addition, the controller 89 is also preferably connected to the pumps78, 80, 84 to control the flow rate of substances flowing to and fromthe separation vessel 28 and the fluid chamber 30. The controller 89preferably maintains a saturated fluidized bed of first particles withinthe fluid chamber 30 to cause second particles to be retained in thefluid chamber 30. The controller 89 may include a computer havingprogrammed instructions provided by a ROM or RAM as is commonly known inthe art.

The controller 89 may vary the rotational speed of the centrifuge rotor12 by regulating frequency, current, or voltage of the electricityapplied to the motor 14. Alternatively, the rotational speed can bevaried by shifting the arrangement of a transmission (not shown), suchas by changing gearing to alter a rotational coupling between the motor14 and rotor 12. The controller 89 may receive input from a rotationalspeed detector (not shown) to constantly monitor the rotation speed ofthe rotor 12.

The controller 89 may also regulate one or more of the pumps 78, 80, 84to vary the flow rates for substances supplied to or removed from theseparation vessel 28 and the fluid chamber 30. For example, thecontroller 89 may vary the electricity provided to the pumps 78, 80, 84.Alternatively the controller 89 may vary the flow rate to and from thevessel 28 and the fluid chamber 30 by regulating valving structures (notshown) positioned in the lines 36, 38, 40, 42, 44 and/or 88. Thecontroller 89 may receive input from a flow detector (not shown)positioned within the first outlet line 38 to monitor the flow rate ofsubstances entering the fluid chamber 30. Although a single controller89 having multiple operations is schematically depicted in theembodiment shown in FIG. 1, the controlling structure of the inventionmay include any number of individual controllers, each for performing asingle function or a number of functions. The controller 89 may controlflow rates in many other ways as is known in the art.

FIG. 4 shows an embodiment of a tubing set 90 a for use in the apparatus10, and FIG. 5 illustrates a cross-sectional view of a portion of thetubing set 90 a mounted in groove 18 a on rotor 12 a. The tubing set 90a includes a separation vessel 28 a, the fluid chamber 30, an inflowtube 36 a for conveying a fluid to be separated, such as whole blood,into the separation vessel 28 a, first, second, and third outlet lines38 a, 40 a, 42 a for removing separated components of the fluid from theseparation vessel 28 a, and an interface control line 44 a for adjustingthe level of an interface between separated substances in the vessel 28a. When the separation vessel 28 a is mounted on a rotor 12 a, the lines36 a, 38 a, 42 a, and 44 a preferably pass through slots (not shown)formed on the rotor 12 a.

Preferably, the separation vessel 28 a is constructed similar to thecentrifugal separator disclosed in above-mentioned U.S. Pat. No.4,647,279 to Mulzet et al. The separation vessel 28 a includes agenerally annular channel 92 a formed of semi-rigid or flexible materialand having a flow path 46 a, shown in FIG. 5. Opposite ends of thechannel 92 a are connected to a relatively rigid connecting structure 94including an inlet portion 48 a and outlet portion 50 a for theseparation vessel 28 a separated by a wall 52 a. An inlet port 54 a ofinflow tubing 36 a is in fluid communication with the inlet portion 48 aand allows for flow of a substance to be separated, such as blood, intothe separation vessel 28 a. During a separation procedure, substancesentering the vessel 28 a via the inlet port 54 a flow around the channel92 a (counterclockwise in FIG. 5) via the flow path 46 a and stratifyaccording to differences in density in response to rotation of the rotor12 a.

The separated substances flow into the outlet portion 50 a where theyare removed through first, second and third outlet ports 56 a, 58 a, and60 a of respective first, second, and third collection lines 38 a, 40 a,and 42 a and an interface control port 61 a of the interface controlline 44 a. As shown in FIG. 5, the second collection line 40 a ispreferably connected to the interface control line 44 a so thatsubstances flowing through the second collection line 40 a and interfacecontrol line 44 a are removed together through a portion of theinterface control line 44 a.

The first, second and third outlet ports 56 a, 58 a, and 60 a and theinterface control port 61 a have the same relative radial positioning asthat of the first, second, and third outlet ports 56, 58, and 60 and theinterface control port 61 shown in FIG. 2, respectively. As shown inFIG. 6, the first port 56 a and interface port 61 a are spaced in theradial direction by a distance“d” of from about 0.035 inch to about0.115 inch so that the first port 56 a is slightly closer to the axis ofrotation A—A.

The outlet portion 50 a includes a barrier 62 a for substantiallyblocking flow of intermediate density substances, such as platelets andsome white blood cells. In the embodiment shown in FIG. 5, the barrier62 a is a skimmer dam extending across the outlet portion 50 a in adirection generally parallel to the axis of rotation A—A. The firstcollection port 56 a is positioned immediately upstream from the skimmerdam 62 a, and downstream from the inlet portion 48 a, to collect theintermediate density substances blocked by the skimmer dam 62 a.

A shield 96 a extends from the upstream side of the skimmer dam 62 a.The shield 96 a is preferably configured like the shield 96 shown inFIG. 2 to limit flow of higher density components into the first port 56a. As shown in FIG. 6, the radially inward surface 98 a of the shield 96a is spaced radially outward from the first outlet port 56 a by a gap“g” of preferably from about 0.005 inch to about 0.08 inch, and morepreferably from about 0.02 inch to about 0.03 inch.

Radially inner and outer edges of the skimmer dam 62 a are spaced fromradially inner and outer walls of the separation vessel 28 a to form afirst passage 64 a for lower density substances, such as plasma, at aradially inner position in the outlet portion 50 a and a second passage66 a for higher density substances, such as red blood cells, at aradially outer position in the outlet portion 50 a. The second and thirdcollection ports 58 a and 60 a are preferably positioned downstream fromthe skimmer dam 62 a to collect the respective higher and lower densitysubstances passing through the first and second passages 66 a and 64 a.

As shown in FIG. 5, a ridge 68 a extends from the inner wall 20 a of thegroove 18 a toward the outer wall 22 a of the groove 18 a. When theseparation vessel 28 a is loaded in the groove 18 a, the ridge 68 adeforms the semi-rigid or flexible material of the separation vessel 28a to form a trap dam 70 a on the radially inner wall of the separationvessel 28 a between the first collection port 56 a and the inlet portionof the separation vessel 28 a. The trap dam 70 a extends away from theaxis of rotation A—A to trap a portion of lower density substances, suchas priming fluid and/or plasma, along a radially inner portion of theseparation vessel 28 a. In addition, the trap dam 70 a has a gradualsloped downstream portion 104 a, and a downstream end 106 a locatedcloser than the first outlet port 56 a to the axis of rotation A—A. Thetrap dam 70 a preferably has the same or substantially the samestructural configuration and function as the trap dam 70 shown in FIG. 2and could be permanent structure formed in the vessel 28 a.

The outer wall 22 a preferably includes a gradual sloped portion 108 afor forming a corresponding gradual sloped segment 110 a in the vessel28 a when the vessel 28 a is deformed in the groove 18. The portion 108a and segment 110 a have the same or substantially the same structuralconfiguration and function as the portion 108 and segment 110 shown inFIG. 2, respectively.

FIG. 7 shows an embodiment of a separation vessel 28 b constructedsubstantially the same as the separation vessel 28 a shown in FIGS. 4-6.In this embodiment, the third collection line 42 b is flow coupled tothe outflow tubing 88 b extending from the fluid chamber outlet 32. Thisplaces the third outlet port 60 a in flow communication with the fluidchamber outlet 32 to thereby mix substances flowing through the thirdoutlet port 60 a with substances flowing through the fluid chamberoutlet 32. During a blood component separation procedure, for example,this structural configuration mixes plasma flowing through third port 60a with platelets and plasma flowing from the fluid chamber 30. Incertain circumstances, this dilution of the platelet collection may bedesired to possibly increase shelf life of the platelet collection.

The fluid chamber outlet 32 and third outlet port 60 a could be flowcoupled in many different ways. For example, the third collection line42 b could coupled to the outflow tubing 88 b upstream from pump 80shown in FIG. 2 to reduce the concentration of particles being pumpedand possibly eliminate pump 84. In the alternative, the outlet of pump84 could be flow coupled to the outlet of pump 80, for example.Preferably, the flow connection of the third collection line 42 b andoutflow tubing 88 b is not located on the rotatable centrifuge rotor 12a.

Methods of separating components or particles of blood are discussedbelow with reference to FIGS. 1, 2, and 7. Although the invention isdescribed in connection with blood component separation processes andthe structure shown in the drawings, it should be understood that theinvention in its broadest sense is not so limited. The invention may beused to separate a number of different particles and/or fluidcomponents, and the structure used to practice the invention could bedifferent from that shown in the drawings. In addition the invention isapplicable to both double needle and single needle blood purification orfiltration applications. For example, the invention may be practicedwith the SINGLE NEEDLE RECIRCULATION SYSTEM FOR HARVESTING BLOODCOMPONENTS of U.S. Pat. No. 5,437,624, the disclosure of which isincorporated herein by reference.

After loading the separation vessel 28 and fluid chamber 30 on the rotor12, preferably, the separation vessel 28 and chamber 30 are initiallyprimed with a low density fluid medium, such as air, saline solution,plasma, or another fluid substance having a density less than or equalto the density of liquid plasma. Alternatively, the priming fluid iswhole blood itself. This priming fluid allows for efficientestablishment of a saturated fluidized bed of platelets within the fluidchamber 30. When saline solution is used, the pump 78 shown in FIG. 2pumps this priming fluid through the inflow line 36 and into theseparation vessel 28 via the inlet port 54. The saline solution flowsfrom the inlet portion 48 to the outlet portion 50 (counterclockwise inFIG. 2) and through the fluid chamber 30 when the controller 89activates the pump 80. Controller 89 also initiates operation of themotor 14 to rotate the centrifuge rotor 12, separation vessel 28, andfluid chamber 30 about the axis of rotation A—A. During rotation,twisting of lines 36, 38, 40, 42, and 88 is prevented by a seallessone-omega/two-omega tubing connection as is known in the art anddescribed in above-mentioned U.S. Pat. No. 4,425,112.

As the separation vessel 28 rotates, a portion of the priming fluid(blood or saline solution) becomes trapped upstream from the trap dam 70and forms a dome of priming fluid (plasma or saline solution) along aninner wall of the separation vessel 28 upstream from the trap dam 70.After the apparatus 10 is primed, and as the rotor 10 rotates, wholeblood or blood components are introduced through the inlet port 54 intothe separation vessel 28. When whole blood is used, the whole blood canbe added to the separation vessel 28 by transferring the blood directlyfrom a donor through inflow line 36. In the alternative, the blood maybe transferred from a container, such as a blood bag, to inflow line 36.

The blood within the separation vessel 28 is subjected to centrifugalforce causing components of the blood components to separate. Thecomponents of whole blood stratify in order of decreasing density asfollows: 1. red blood cells, 2. white blood cells, 3. platelets, and 4.plasma. The controller 89 regulates the rotational speed of thecentrifuge rotor 12 to ensure that this particle stratification takesplace. A layer of red blood cells (high density component(s) H) formsalong the outer wall of the separation vessel 28 and a layer of plasma(lower density component(s) L) forms along the inner wall of theseparation vessel 28. Between these two layers, the intermediate densityplatelets and white blood cells (intermediate density components I) forma buffy coat layer. This separation takes place while the componentsflow from the inlet portion 48 to the outlet portion 50. Preferably, theradius of the flow path 46 between the inlet and outlet portions 48 and50 is substantially constant to maintain a steady red blood cell bed inthe outlet portion 50 even if flow changes occur.

In the outlet portion 50, platelet poor plasma flows through the firstpassage 64 and downstream of the barrier 62 where it is removed via thethird collection port 60. Red blood cells flow through the secondpassage 66 and downstream of the barrier 62 where they are removed viathe second collection port 58. After the red blood cells, white bloodcells, and plasma are thus removed, they are collected and recombinedwith other blood components or further separated. Alternately, theseremoved blood components may be reinfused into a donor.

The higher density component(s) H (red blood cells) and lower densitycomponent(s) L (plasma) are alternately removed via the interfacecontrol port 61 to control the radial position of the interface Fbetween the higher density component(s) H and intermediate densitycomponent(s) I (buffy layer). This interface control preferablymaintains the radially inner shield surface 98 between the interface Fand first outlet port 56.

A substantial portion of the platelets and some of the white blood cellsaccumulate upstream from the barrier 62. The accumulated platelets areremoved via the first outlet port 56 along with some of the white bloodcells and plasma. The shield 96 limits passage of higher densitysubstances H (red blood cells) into the first outlet port 56.Preferably, the shield 96 substantially reduces the number of red bloodcells entering the first outlet port 56, thereby improving collectionpurity.

As the platelets, plasma, white blood cells, and possibly a small numberor red blood cells pass through the first outlet port 56, thesecomponents flow into the fluid chamber 30, filled with the primingfluid, so that a saturated fluidized particle bed may be formed. Theportion or dome of priming fluid (i.e. saline) trapped along the innerwall of the separation vessel 28 upstream from the trap dam 70 guidesplatelets so that they flow toward the barrier 62 and the first outletport 56. The trapped fluid reduces the effective passageway volume andarea in the separation vessel 28 and thereby decreases the amount ofblood initially required to prime the system in a separation process.The reduced volume and area also induces higher plasma and plateletvelocities next to the stratified layer of red blood cells, inparticular, to“scrub” platelets, toward the barrier 62 and first outletport 56. The rapid conveyance of platelets increases the efficiency ofcollection.

During a blood component separation procedure, the priming fluid trappedupstream from the trap dam 70 may eventually be replaced by other fluidssuch as low density, platelet poor plasma flowing in the separationvessel 28. Even when this replacement occurs, a dome or portion oftrapped fluid is still maintained upstream from the trap dam 70.

The relatively gradual slope of the downstream portion 104 of the trapdam 70 limits the number of platelets that become reentrained withplasma as plasma flows along the trap dam 70. The downstream portion 104also reduces the number of platelets accumulated upstream from thebarrier 62.

The gradually sloped segment 110 causes formation of a layer of redblood cells across from the trap dam 70. The segment 110 maintainsrelatively smooth flow transitions in the separation vessel 28 andreduces the velocity of red blood cells in this region.

During a blood component separation procedure, a bed of red blood cellsis preferably maintained along the radial outer wall 65 of theseparation vessel 28 between the inlet and outlet portions 48 and 50. Inaddition, the dome or portion of fluid trapped by the trap dam 70 ispreferably maintained along the radial inner wall 63 of the separationvessel 28. The bed of red blood cells and trapped fluid substantiallylimit, or more preferably prevent, platelets from contacting radiallyouter and inner walls 65 and 63, respectively, because the platelets aresandwiched between the red blood cell bed and trapped fluid. This isbelieved to reduce platelet clumping caused when platelets come incontract with structural components of centrifugal separation devices,which are formed of conventional polymer materials. Reduction ofplatelet clumping is significant because it allows for separation of agreater amount of blood components and does not require the use of asmuch anticoagulant (AC). For example, the present invention is believedto allow for processing of about 20% more blood, as compared to someconventional dual-stage centrifugal separation devices. In addition, thepresent invention allows for the use of about a 12 to 1 volume ratio ofblood components to AC as compared to a 10 to 1 ratio normally used forsome conventional dual-stage centrifugal separation devices, forexample.

Accumulated platelets, white blood cells, and some plasma and red bloodcells, are removed via the first outlet port 56 and flow into the fluidchamber 30 so that the platelets form a saturated fluidized particlebed. The controller 89 maintains the rotation speed of the rotor 12within a predetermined rotational speed range to facilitate formation ofthis saturated fluidized bed. In addition, the controller 89 regulatesthe pump 80 to convey at least the plasma, platelets, and white bloodcells at a predetermined flow rate through the first collection line 38and into the inlet 34 of the fluid chamber 30. These flowing bloodcomponents displace the priming fluid from the fluid chamber 30.

When the platelet and white blood cell particles enter the fluid chamber30, they are subjected to two opposing forces. Plasma flowing throughthe fluid chamber 30 with the aid of pump 80 establishes a first viscousdrag force when plasma flowing through the fluid chamber 30 urges theparticles toward the outlet 32. A second centrifugal force created byrotation of the rotor 12 and fluid chamber 30 acts to urge the particlestoward the inlet 34.

The controller 89 preferably regulates the rotational speed of the rotor12 and the flow rate of the pump 80 to collect platelets and white bloodcells in the fluid chamber 30. As plasma flows through the fluid chamber30, the flow velocity of the plasma decreases and reaches a minimum asthe plasma flow approaches the maximum cross-sectional area of the fluidchamber 30. Because the rotating centrifuge rotor 12 creates asufficient gravitational field in the fluid chamber 30, the plateletsaccumulate near the maximum cross-sectional area of the chamber 30,rather than flowing from the chamber 30 with the plasma. The white bloodcells accumulate somewhat radially outward from the maximumcross-sectional area of the chamber 30. However, density inversion tendsto mix these particles slightly during this initial establishment of thesaturated fluidized particle bed.

The larger white blood cells accumulate closer to inlet 34 than thesmaller platelet cells, because of their different sedimentationvelocities. Preferably, the rotational speed and flow rate arecontrolled so that very few platelets and white blood cells flow fromthe fluid chamber 30 during formation of the saturated fluidizedparticle bed.

The platelets and white blood cells continue to accumulate in the fluidchamber 30 while plasma flows through the fluid chamber 30. As theconcentration of platelets increases, the interstices between theparticles become reduced and the viscous drag force from the plasma flowgradually increases. Eventually the platelet bed becomes a saturatedfluidized particle bed within the fluid chamber 30. Since the bed is nowsaturated with platelets, for each new platelet that enters thesaturated bed in the fluid chamber 30, a single platelet must exit thebed. Thus, the bed operates at a steady state condition with plateletsexiting the bed at a rate equal to the rate additional platelets enterthe bed after flowing through inlet 34.

The saturated bed establishes itself automatically, independent of theconcentration of particles flowing into the fluid chamber 30. Plasmaflowing into the fluid chamber 30 passes through the platelet bed bothbefore and after the platelet saturation point.

The saturated bed of platelets occupies a varying volume in the fluidchamber 30 near the maximum cross-sectional area of the chamber 30,depending on the flow rate and centrifugal field. The number ofplatelets in the saturated bed depends on a number of factors, such asthe flow rate into the fluid chamber 30, the volume of the fluid chamber30, and rotational speed. If these variables remain constant, the numberof platelets in the saturated fluidized bed remains substantiallyconstant. When the flow rate of blood components into the fluid chamber30 changes, the bed self adjusts to maintain itself by either releasingexcess platelets or accepting additional platelets flowing into thefluid chamber 30. For example, when the plasma flow rate into the fluidchamber 30 increases, this additional plasma flow sweeps excessplatelets out of the now super-saturated bed, and the bed reestablishesitself in the saturated condition at the increased flow rate. Therefore,the concentration of platelets in the bed is lower due to the release ofbed platelets.

After the saturated fluidized bed of platelets forms, flowing plasmacarries additional platelets into the fluid chamber 30 and the bed.These additional platelets add to the bed and increase the viscous dragof the plasma flow through the bed. At some point the viscous drag issufficient to cause platelets near the maximum cross-section area of thefluid chamber 30 to exit the saturated bed and fluid chamber 30. Thus,if the rotational speed and flow rate into the fluid chamber 30 remainconstant, the number and concentration of platelets flowing into thesaturated fluidized bed of platelets substantially equals the number andconcentration of platelets released from the bed.

Although the bed is saturated with platelets, a small number of whiteblood cells may be interspersed in the platelet bed. These white bloodcells, however will tend to “fall” or settle out of the platelet bedtoward inlet 34 due to their higher sedimentation velocity. Most whiteblood cells generally collect within the fluid chamber 30 between thesaturated platelet bed and the inlet 34.

Red blood cells in the fluid chamber 30 also settle toward the fluidchamber inlet 34, and some of the red blood cells preferably exit thefluid chamber 30 via the inlet 34 while blood components are enteringthe chamber 30 via the inlet 34. In other words, bidirection flow intoand out of the fluid chamber 30 may take place at the fluid chamberinlet 34.

The controller 89 preferably controls the pump 80 to limit the number ofred blood cells accumulating in the fluid chamber 30. For example, thecontroller 89 can temporarily reverse flow of the pump 80 to cause redblood cells and other dense substances to be flushed from the fluidchamber outlet 34. In addition, the controller 89 may cycle the pump 80to allow for accumulation of relatively sparse components, such as whiteblood cells, upstream from the barrier 62.

The saturated fluidized bed of platelet particles formed in the fluidchamber 30 functions as a filter or barrier to white blood cells flowinginto the fluid chamber 30. When blood components flow into the fluidchamber 30, plasma freely passes through the bed. However, the saturatedfluidized platelet bed creates a substantial barrier to white bloodcells entering the fluid chamber 30 and retains these white blood cellswithin the fluid chamber 30. Thus, the bed effectively filters whiteblood cells from the blood components continuously entering the fluidchamber 30, while allowing plasma and platelets released from thesaturated bed to exit the chamber 30. This replenishment and release ofplatelets is referred to as the bed's self-selecting quality.Substantially all of these filtered white blood cells accumulate withinthe fluid chamber 30 between the saturated fluidized platelet bed andthe inlet 34.

The particle separation or filtration of the saturated fluidizedparticle bed obviates a number of limitations associated with prior artelutriation. For example, particles may be separated or filtered in acontinuous steady state manner without batch processing. In addition, anadditional elutriating fluid medium is not required. Furthermore, afterthe saturated fluidized particle bed is established, flow rates may bevaried over a range without changing the size of the particles leavingthe fluid chamber 30. Unlike prior art elutriation, the presentinvention establishes a saturated particle bed consisting of numericallypredominant particles. This bed automatically passes the predominantparticles while rejecting larger particles.

The apparatus and method of the invention separate substantially all ofthe white blood cells from the platelets and plasma flowing through thefluid chamber 30. The barrier to white blood cells is created, at leastin part, because white blood cells have a size and sedimentationvelocity greater than that of the platelets forming the saturatedfluidized particle bed. Therefore, particles of similar densities areseparated according to different sizes or sedimentation velocities.

Because the initial separation at barrier 62 and the saturated fluidizedbed remove a majority of the red blood cells and some white blood cells,the fluid exiting the fluid chamber 30 consists mainly of plasma andplatelets. Unlike some conventional porous filters, where the filteredwhite blood cells are retained in the filter, the present inventionallows a substantial fraction of white blood cells to be recovered andreturned to the donor.

When the blood components are initially separated within the separationvessel 28, a substantial number of platelets may become slightlyactivated. The saturated fluidized platelet bed allows white blood cellsto be filtered from plasma and platelets despite this slight activation.Thus, the present invention does not require a waiting period to filterwhite blood cells after blood components undergo initial separation in aseparation vessel 28. This is in contrast to methods using someconventional filters.

After separation, the platelets and plasma exiting the fluid chamber 30are collected in appropriate containers and stored for later use. Thered blood cells and plasma removed from the vessel 28 may be combinedfor donor reinfusion or storage. Alternatively, these components may befurther separated by the apparatus 10.

If dilution of the platelet concentration is desired, the separationvessel 28 b shown in FIG. 7 may be used to combine plasma removed viathe third outlet port 60 a with the platelets and plasma flowing fromthe fluid chamber outlet 32. This allows for the dilution to take placerapidly without significant intervention by a procedurist.

At the completion of a separation procedure, platelets in the saturatedfluidized bed are harvested to recover a substantial number of plateletsfrom the fluid chamber 30. During bed harvest, the controller 89increases the flow rate and/or decreases the rotational speed of therotor 12 to release platelets from the bed. This flushes from the fluidchamber 30 most of the platelets that made up the saturated fluidizedbed to substantially increase platelet yield. The harvesting continuesuntil substantially all of the platelets are removed, and just before anunacceptable number of white blood cells begin to flow from the fluidchamber 30.

The remainder of contents of the fluid chamber 30, having a highconcentration of white blood cells, can be separately collected forlater use or recombined with the blood components removed from vessel 28for return to a donor.

Although the inventive device and method have been described in terms ofremoving white blood cells and collecting platelets, this description isnot to be construed as a limitation on the scope of the invention. Theinvention may be used to separate any of the particle components ofblood from one another. For example, the saturated fluidized bed may beformed from red blood cells to prevent flow of white blood cells throughthe fluid chamber 22, so long as the red blood cells do not rouleau(clump) excessively. Alternatively, the liquid for carrying theparticles may be saline or another substitute for plasma. In addition,the invention may be practiced to remove white blood cells or othercomponents from a bone marrow harvest collection or an umbilical cordcell collection harvested following birth. In another aspect, theinvention can be practiced to collect T cells, stem cells, or tumorcells. Further, one could practice the invention by filtering orseparating particles from fluids unrelated to either blood orbiologically related substances.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure andmethodology of the present invention without departing from the scope orspirit of the invention. For example, the fluid chamber 30 of theinvention may be used in a separation process involving elutriation orany other particle separation means without departing from the scope ofthe invention. Certain aspects of the invention could also be practicedwithout the fluid chamber. The invention, in its broadest sense, mayalso be used to separate many different types of particles and/orcomponents from one another. In addition, the above-mentioned separationvessels 28, 28 a, and 28 b may be generally belt shaped and have theinlet portion and outlet portion in separate ends spaced from oneanother without having the inlet portion connected directly to theoutlet portion to form a generally annular shape. Thus, it should beunderstood that the invention is not limited to the examples discussedin this specification. Rather, the invention is intended to covermodifications and variations provided they come within the scope of thefollowing claims and their equivalents.

What is claimed is:
 1. A method of separating components of a fluid, themethod comprising: rotating a separation vessel about an axis ofrotation; passing fluid to be separated into the vessel; separating thefluid in the rotating separation vessel into at least a relatively highdensity component, relatively intermediate density components, and arelatively low density component, the intermediate density componentsincluding at least a first subcomponent and a second subcomponent;removing at least the relatively intermediate density components fromthe separation vessel via a first outlet port in the separation vessel;flowing the removed intermediate density components into a fluidchamber; retaining at least some of the first subcomponent in the fluidchamber; permitting at least some of the second subcomponent to flowfrom an outlet of the fluid chamber; removing at least some of the lowdensity component from the separation vessel via a second outlet port inthe separation vessel; and combining the low density component removedfrom the separation vessel with the second subcomponent flowing from theoutlet of the fluid chamber.
 2. The method of claim 1, wherein the highdensity component includes red blood cells, the first subcomponentincludes white blood cells, the second subcomponent includes platelets,and the low density component includes plasma.
 3. The method of claim 1,further comprising removing the high density component from theseparation vessel via a third outlet port in the separation vessel. 4.The method of claim 1, further comprising accumulating at least theintermediate density components with a barrier in the separation vessel,the accumulated intermediate density components being removed from theseparation vessel via the first outlet port.
 5. The method of claim 4,further comprising flowing the high density component and the lowdensity component past the barrier.
 6. The method of claim 1, furthercomprising forming in the fluid chamber a saturated fluidized particlebed including the second subcomponent, the saturated fluidized bedretaining at least the first subcomponent in the fluid chamber.
 7. Themethod of claim 1, further comprising accumulating some of the lowdensity component with a trap dam in the separation vessel.
 8. Themethod of claim 1, further comprising separating the first and secondsubcomponents in the fluid chamber by elutriation.
 9. The method ofclaim 1, wherein the combining comprises flowing both the low densitycomponent removed from the separation vessel and the second subcomponentflowing from the outlet of the fluid chamber into a flow coupling inflow communication with both the second outlet port in the separationvessel and the outlet of the fluid chamber.
 10. The method of claim 1,wherein said combining occurs during said rotating.
 11. The method ofclaim 1, wherein said combining occurs during said permitting.
 12. Themethod of claim 1, wherein said combining occurs during said removing atleast some of the low density component from the separation vessel.